The base level interior rearview mirror element for a vehicle is often a prismatic rearview mirror element, which may provide a low cost complete mirror assembly for the vehicle. The complete mirror assembly is often economically assembled by snapping or inserting the toggle assembly and prismatic reflective element into the casing at the front or bezel portion of the mirror casing substantially immediately after the casing (which may be formed of a hot molded polypropylene or the like) is formed and while the casing is still hot and pliable. It is often desirable to provide an electronic feature in the mirror assembly, such as an accessory and an associated display and/or the like. Other complete mirror assembly types are known in the art, such as two piece housing assemblies, such as described in U.S. Pat. Nos. 5,178,448; 5,649,756; 6,329,925; and 6,501,387, which are hereby incorporated herein by reference.
Typically, when manufacturing a prismatic reflective element, the reflective layer (typically a silver mirror reflector layer overcoated with a copper corrosion resistant layer and protected with a several mil thick protective paint layer, all applied on a chemical silvering line, as known in the mirror art) is first applied to a surface of approximately 6 mm thick flat float soda lime glass, typically on the air side of the float glass, where the surface is a high quality, smooth, substantially scratch free, pristine surface. The layer of paint that is applied over the silvering layer protects the reflective layer from mechanical/physical damage during subsequent processing of the silvered float glass to form an automotive interior prismatic mirror element shape.
Thus, the first stage of a glass automotive prismatic element manufacturing process comprises flat glass that is silvered on a second surface that opposes a first, unsilvered glass surface (wherein the first surface is the side of the glass element that ultimately generally faces and is closest to a driver of the vehicle when the complete mirror assembly is installed in the vehicle, while the second surface is opposite to/opposing the first surface). The first glass surface is then ground, such as by diamond wheel grinding while the silvered/paint protected glass side is held on a chuck or fixturing device, or while the silvered/paint protected glass is conveyed through an in-line grinding process with the silvered/painted surface contacting the conveying element, such as rollers or the like, and finely polished to create a glass surface now slanted at approximately a three to four degree prism angle relative to the second or silvered surface, while the layer of paint protects the reflective/silvered layer from damage during the grinding/polishing of the first glass surface.
Conventional paint systems are absorbing, such that the painted/silvered prism element is non-transparent. Thus, and such as described in U.S. Pat. No. 5,285,060, which is hereby incorporated herein by reference, it is known to create a window, such as by sandblasting or laser ablation or the like, in the painted/silvered layers for a display element to display information through the window and through the prism for viewing by a driver of the vehicle. However, this removes the protective paint and the silvered layers from the rear surface of the prism.
Therefore, there is a need in the art for an improved prismatic reflective element for a mirror assembly which overcomes the shortcomings of the prior art.